Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$20.98	4.481%	$21.9201	$21.92	$21.90	$21.90
Purchase #2	$79.32	13.622%	$90.125	$90.13	$90.15	$90.10
Purchase #3	$17.91	5.133%	$18.8293	$18.83	$18.85	$18.80
Purchase #4	$64.29	9.557%	$70.4342	$70.43	$70.45	$70.40
Purchase #5	$66.43	10.742%	$73.5659	$73.57	$73.55	$73.60
Purchase #6	$237.88	5.806%	$251.6913	$251.69	$251.70	$251.70
Purchase #7	$38.90	5.797%	$41.155	$41.16	$41.15	$41.20
7 purchase totals =	$525.71		$567.7208	$567.73	$567.75	$567.70